We report a significant enhancement of proton-boron (p- 11 B) fusion yield driven by a high-current proton beam, mediated by the formation of a transient target plasma. In experiments at the Institute of Modern Physics, Chinese Academy of Sciences, proton beams were incident on solid carbon-hydrogen-boron targets. Crucially, under high-current conditions, the normalized alpha-particle yield increased by approximately 1.48 times and 1.75 times for alpha 0 and alpha 1 , respectively, compared to low-current runs. We attribute this non-linear scaling with beam current to a fundamental shift in the interaction regime: the intense beam energy deposition transforms the target surface into a localized weakly ionized plasma. This plasma state dramatically increases the probability and observable yield of the p- 11 B reaction. This result provides direct experimental evidence that beam-induced plasma formation is a powerful method to boost alpha-particle yields in solid-target experiments, highlighting the dynamic role of the target and opening new parameter spaces for optimizing aneutronic fusion schemes.
Yb:YAG thin-rod crystals with high optical gain, excellent thermal and mechanical properties represent a promising gain medium for high-power ultrafast lasers and amplifiers near 1 mu m. However, the impacts of critical thin-rod parameters, including crystal length, Yb3+ doping concentration, bonding configuration, and cooling temperature, on amplifier performance are incompletely understood. Here, we systematically investigate these parameters in a single-stage double-pass Yb:YAG thin-rod picosecond amplifier seeded by a 1030 nm picosecond fiber laser. The seed source provides 11.5 ps pulses at 1030 nm with a repetition rate of 396 kHz. Six Yb:YAG thin-rod samples with varying bonding configurations, doping concentrations, lengths, and cooling temperatures are characterized. The optimal performance is achieved using a double-end-bonded thin rod with 3-mm undoped end caps, a length of 25 mm, a doping concentration of 2% (atomic fraction), and a cooling temperature of 288 K. Using these optimal parameters, the average power is amplified from 326 mW to 17.7 W, corresponding to a power gain of 17 dB, while preserving near-diffraction-limited beam quality (M-2<1.2). These results offer valuable guidance for the selection and optimization of Yb:YAG thin rods in high-power single-stage double-pass picosecond amplifiers.
We present a miniaturized laser frequency-stabilization module based on the 87Rb 5S1/2 -> 5D5/2 two-photon transition. A 778 nm external-cavity diode laser excites the atoms in a small vapor cell, and the generated 420 nm fluorescence provides the stabilization for closed-loop feedback. The optical system-including micro-optics, a vapor cell, and a heater-is fully integrated on a 3D-printed nylon substrate with a total volume of 20 cm3 and a weight of 10.4 g. By optimizing the structure and stabilization scheme, we obtain a high-signal-to-noise ratio (SNR) fluorescence signal and an error signal. The stabilized laser reaches fractional frequency stability of 1.1 & times; 10-11 @ 1 s and 2.89 & times; 10-13 @ 100 s.
Intense narrowband terahertz (THz) radiation can facilitate advancements in engineering and scientific applications. In this study, we propose a novel scheme to generate coherent narrowband THz wakefield radiation by combining a beatwave pre-bunching technique with dielectric-lined waveguide structures. Start-to-end three-dimensional simulations demonstrate that a 1 nC electron bunch can generate a radiation pulse of 210 & micro;J at 2.08 THz with a relative bandwidth of 0.43%. The results confirm the flexibility and adjustability of the proposed scheme in frequency tuning and precise mode control, establishing it as a viable method for generating intense narrowband THz pulses in free-electron laser facilities.
This work presents a combined modeling and experimental study of radiation-induced loss in thulium-doped fiber amplifiers (TDFAs) under gamma-ray irradiation. Within the experimental dose range of 0-5 krad(Si), the attenuation of both pump and signal lights increases approximately linearly with total dose, with the pump light exhibiting greater sensitivity. Consequently, the output power decreases approximately linearly with dose. Good agreement between the modeled and measured output power is achieved using key parameters extracted from experiments. Furthermore, fibers with higher Ge/Al molar ratios exhibit enhanced radiation resistance, guiding the design of radiation-hardened thulium-doped fibers.
Petawatt-class femtosecond laser interaction with a pitcher-catcher target in the presence of a prepulse is investigated using self-consistent integrated simulations. We demonstrate that under typical laser contrast conditions, superponderomotive hot electrons from betatron-like resonance absorption in the preplasma significantly enhance the acceleration of protons and deuterium ions, leading to an effective increase in neutron yield. A beryllium converter serving as the catcher layer offers superior performance in improving neutron source quality. For experimental practicality, a novel converter is proposed, in which beryllium is encapsulated in lithium-hydrogen ceramic to ensure safe radiation emission levels while achieving a high retention rate. In particular, with a laser intensity of 4 x 10(21) W/cm(2), a duration of 30 fs, and a power of 1.45 PW, the proposed converter enables the generation of a short-pulse neutron source with a forward yield as high as 1.08 x 10(10) neutrons/sr and a maximum energy of similar to 70 MeV, where the forward component accounts for up to 70% of the total neutron yield. Such a high-quality neutron source, capable of operating at hertz-level repetition rates, is promising for industrial non-destructive testing and related applications.
We report a high-beam-quality high-power green laser source via second-harmonic generation (SHG) driven by a coherently combined femtosecond laser. An 82 W average output power at 515 nm is obtained with a 200 kHz repetition rate and a 400 fs pulse duration. Using a 1.5-mm-thick beta-barium borate (BBO) crystal, a conversion efficiency of 63% is achieved at an input power of 130 W. The system delivers near diffraction-limited beam quality, exhibiting M2 = 1.13 & times; 1.14 and power stability characterized by a root-mean-square (RMS) fluctuation of 0.86% over 1 h. The outstanding spatiotemporal characteristics of the green laser output highlight the clear advantage of the coherently combined beam in nonlinear frequency conversion.
